Aluminum base alloy casting



United States Patent 3,161,502 ALUMINUM BASE ALLQY CASTENG Harold Y. Hunsicker, New Kensington, Pa, and Robert C. Lemon, Cleveland, Ohio, assignors to Aluminum Company of America, Pittsburgh, Pa., in corporation of Pennsylvania No Drawing. Filed Feb. 25, @635, Ser. No. 260,866 9 Claims. ((Jl. '75143) This invention relates to aluminum base alloys containing low melting alloying. constituents, and particularly, to improve alloys of this nature which are espe cially suitable for use in production of cast products for bearing applications.

Commercial products of aluminum alloys containing nominally 6 to 7% tin and a small percentage of suitable hardening elements are produced in the form or" sand castings and permanent mold castings for use in bearing applications. However, when such an alloy is cast there is a strong tendency toward hot shortness. This liability to crack or tear is attributable to the interdendritic or intergranular network of tin in the aluminum This tendency to hot shortness not only has limited the economical production of die castings, but sand castings and permanent mold castings as well. The same tendency to be hot short is also found in castings of the aluminum-% silicon-4% copper alloy type to which tin has been added to improve the bearing characteristics.

We have found that the adverse eiiect of the tin in forming an interdendritic film 'in the aluminum-siliconcopper type alloy may be suppressed thereby rendering.

the alloyamenable to casting ope-rations. In accordance with our invention this film forming tendency of tin in the aluminum matrix is suppressed by the addition of cadmium and lead to the alloy. The total amount of cadmium and lead added should at leastequal, or be greater than, the tin content. Our new aluminum base alloy containing tin, lead and cadmium as low melting point components is therefore suitable for making castings, especially die castings, but may also include permanent mold castings, and sand castings, particularly those sand castings having an intricate shape.

Accordingly, it is the principal object of this invention to provide an improved aluminum-silicon-copper base alloy containing low melting alloy constituents composed of tin, lead and cadmium, which exhibits substantial freedom from hot shortness upon casting, and possesses good bearing characteristics.

In accordance with the present invention the foregoing and other objects and advantages are attained to a particularly high degree in castings of an aluminum base alloy comprising 1.0 to 12% silicon, 0.5 to 6% copper, 0.2 to 3% tin, 0.2 to 5% cadmium and 0.2 to 2% lead, the balance aluminum and incidental impurities. Reference is had herein, and in the appended claims, to percent composition by weight. Alloys containing from about 2 to 12% silicon are particularly suited for the production of die cast articles. In any'case, the total amount of lead plus cadmium must equal or exceed the tin content irrespective ofthe silicon and copper content of the alloy. Castings of an alloy of this composition are characterized by improved anti-friction qualities as compared to castings of the same alloy devoid of the lead and cadmium. The addition of cadmium, lead and-tin to the alloy also increases the resistance to scufling and'galling necessary hardness and strength for bearing purposes.

According to preferred practice the minimum amounts of the two elements should not be used at the same time but rather that if the alloy is to contain the minimum or close to the minimum or" one of the elements, the amount of the other should substantially exceed the minimum.

7 In particular it has been found that castings containing less than 2% of copper and larger amounts of silicon are less susceptible to porosity than those which contain larger amounts of copper.

In order to obtain the desired bearing qualities, it is necessary that the alloy have a total minimum content of cadmium, lead and tin of about 0.6% by weight, and preferably more than about 1.5%, and in the relative proportions of tin to cadmium and lead set forth above. On the other hand, if the amount of tin is in excess of 3%, excessive hot shortness will result and consequently will interfere with the production of sound castings. Also, extensive hot shortness will occur when the tin content exceeds that of the total of cadmium plus lead and the resulting alloy will not be suitable for casting purposes.

Cadmium has a limited liquid solubility in aluminum, and there is a tendency for the cadmium to settle or segregate by gravity unless precautions are taken to avoid it. Lead exhibits a similar solubility. However, when both cadmium and'lead are simultaneously employed in our composition a greater total amount of the two elements can be dissolved at a given melting temperature than either element singly and relatively low pouring temperatures may be employed in casting the alloy. In addition, the simultaneous presence of the three low melting elements produces an eutectic having a lower melting point than that produced by the combination of any two of the elements which is advanta eous in bearing alloys.

The usual incidental impurities found in aluminum ingots or" commercial grade may be included without any substantial detrimental effects. For all castings except die castings, impurities such as iron, manganese, nickel,

magnesium, zinc or titanium should not exceed a total of more than 2% by weight, and except for the zinc, no single. such impurity of this group should be permitted in 2%. Here the iron aids in overcoming the tendency of damage to the bearing surfaces as compared to the behavior of castings of the alloy without these elements.

Aluminum-copper-silicon alloys, which are common in the casting field, exhibit high strength properties, and

in our improved alloy the presence of the copper and silicon increases the load carrying capacity and wear resistance of the bearings. Amounts of siliconand copper the aluminum to adhere to the die or mold, commonly referred to as die soldering.

As an example of our alloy possessing good casting characteristics and bearing qualities is one nominally consisting of 5% silicon, 4% copper, and 0.7% each of tin, cadmium and lead, and the balance aluminum plus incidental impurities. The alloy was die cast at 1200 1250 F. in the form of connecting rods for a refrigeration compressor. These rods performed satisfactorily in a two horsepower compressor under a bearing pressure of 1500 pounds per square inch of projected area. These conditions were too severe for similar die cast rods of an aluminum base alloy nominally composed of aluminum,

3.5% copper and 9.0% silicon which failed under the same conditions. The connecting rods of this alloy could operate successfully only under a bearing pressure of 900 pounds per square inch of projected area with a reduction in power to one horsepower.

illustrated in the following examples where cover plates TABLE I Composition of Alloys, Percent Alloy Silicon Copper Iron Lead Cadmium Tin A total of 50 castings were made from each alloy and all were inspected by the standard dye penetrant method, the number of castings having cracks and the number of cracks being noted. The results of the inspection are given below in Table 11.

TABLE II Cracks in Castings N o. of No. of Alloy Castings Cracks in Having Castings Cracks None None None None 1 1 25 55 It is evident that where the total of lead and cadmium exceeded tin, no cracks occurred but when the proportions were reversed, cracks appeared.

Our new alloy, having the above described properties, may be used for a large number of applications where good bearing qualities are required. Our improved alloy in cast form is particularly desirable for use in connecting rods and crank shaft bearings in internal combustion engines or for air conditioning and refrigerator compressors. In addition, the bearing alloy may be employed in making electric motor end bells, Washing machine and dryer gear housings and parts for other mechanical appliances and hand power tools, such as drills, saws, and the like. In each instance the necessity for separate bearings is eliminated. Tests of bearings made of the'alloys above described have demonstrated relative absence of wear.

This is a continuation-in-part of United States patent application Serial No. 781,949, filed December 22, 1958. We claim:

1. A casting composed of an aluminum base alloy consisting of 0.5 to 6% copper, 1.0 to 12% silicon, 0.2 to 3% tin, 0.2 to 2% lead, 0.2 to cadmium and the balance aluminum and impurities, the total amount of lead plus cadmium being not less than the tin content, said casting being characterized by higher anti-friction properties and substantial freedom from hot shortness than the same composition devoid of said cadmium and lead components.

2. An aluminum base alloy die casting composed of an alloy consisting of 2 to 6% copper, 2 to 12% silicon, 0.2 to 3% tin, 0.2 to 2% lead, 0.2 to 5% cadmium and the balance aluminum and impurities, the total amount of lead plus cadmium being not less than the tin content, said casting characterized by higher anti-friction properties and substantial freedom from hot shortness than the same composition devoid of said lead and cadmium components.

3. An aluminum base alloy die casting consisting of an alloy composed of 2 to 6% copper, 2 to 12% silicon, 0.2 to 3% tin, 0.2 to 2% lead, 0.2 to 5% cadmium, and up to about 2% iron, the balance aluminum and impurities other than iron, the total amount of lead plus cadmium being not less than the tin content, said casting characterized by higher anti-friction properties and substantial freedom from hot shortness than the same composition devoid of said lead and cadmium components.

4. A cast bearing composed of an alloy consisting of 0.5 to 6% copper, 1.0 to 12% silicon, 0.2 to 3% tin, 0.2 to 2% lead, 0.2 to 5% cadmium and the balance aluminum and impurities, the total content of lead plus cadmium being not less than the tin content, said bearing characterized by higher anti-friction properties and substantial freedom from hot shortness than the same composition devoid of said lead and cadmium components.

5. A cast bearing formed from an alloy capable of being die cast consisting of 2 to 6% copper, 2 to 12% silicon, 0.2 to 3% tin, 0.2 to 2% lead, 0.2 to 5% cadmium and the balance aluminum and impurities, the minimum total amount of said tin, lead and cadmium being 1.5% and the total amount of lead plus cadmium is not less than the tin content, said bearing characterized by higher antifriction properties and substantial freedom from hot shortness than the same composition devoid of said lead and cadmium components.

6. A cast bearing formed from an alloy capable of being die cast consisting of 2 to 6% copper, 2 to 12% silicon, 0.2 to 3% tin, 0.2 to 2% lead, 0.2 to 5% cadmium, and up to 2% iron, the balance aluminum and impurities other than iron, the minimum total amount of said tin, lead and cadmium being 1.5% and the total amount of lead plus cadmium is not less than the tin content, said bearing characterized by higher anti-friction properties and substantial freedom from hot shortness than the same composition devoid of said cadmium and lead components.

7. A die cast bearing formed from an alloy consisting of 4% copper, 5% silicon, 0.7% tin, 0.7% lead, 0.7% cadmium and the balance aluminum and impurities, said bearing characterized by higher anti-friction properties and substantial freedom from hot shortness than the same composition devoid of said cadmium and lead components.

8. A casting according to claim 1 wherein the total amount of tin, lead and cadmium is not less than 1.5%.

9. A die casting according to claim 2 wherein the total amount of tin, lead and cadmium is not less than 1.5%

References Cited in the file of this patent UNITED STATES PATENTS 2,076,567 Kemp et al. Apr. 13, 1937 2,076,571 Kemp et al. Apr. 13, 1937 2,473,060 Hunsicker et al June 14, 1949 

1. A CASTING COMPOSED OF AN ALUMINUM BASE ALLOY CONSISTNG OF 0.5 TO 6% COPPER, 1.0 TO 12% SILICON, 0.2 TO 3% TIN, 0.2 TO 2% LEAD, 0.2 TO5% CADMIUM AND THE BALANCE ALUMINUM AND IMPURITIES, THE TOTAL AMOUNT OF LEAD PLUS CADMIUM BEING NOT LESS THAN THE TIN CONTENT, SAID CASTING BEING CHARACTERIZED BY HIGHER ANTI-FRICTION PROPERTIES AND SUBSTANTIAL FREEDOM FROM HOT SHORTNESS THAN THE SAME COMPOSITION DEVOID OF SAID CADMIUM AND LEAD COMPONENTS. 